1. Field of the Invention
The present invention relates to a color reproduction method and system, and a video display device using the same.
2. Background of the Related Art
Generally, a color television system includes a broadcasting station for transmitting broadcast signals that are produced using cameras, and a color television set for processing and reproducing the broadcast signals transmitted from the broadcasting station to allow the audience to see and hear sounds and pictures.
In the development of the color television system, the goal is to obtain the reproduced video proportional to luminance of an original object and to reproduce color equal to a chromaticity coordinate of the original object. For example, in case of a National Television System Committee (NTSC) color television system that employs NTSC standard, a broadcasting camera for capturing videos obtains an ideal imaging characteristic based on an NTSC standard monitor, and a color television set reproduces the same chromaticity coordinate as an original object irradiated by an illuminant C.
However, in most color television sets, reference white and phosphor have been changed differently from the NTSC standard. The reason is that a screen was dark because of a low luminous efficiency of phosphor at that time when the NTSC standard was established, and thus a phosphor with high luminous efficiency was used. At the same time, there were attempts to realize much brighter screen by increasing a chromaticity temperature. For these reasons, American and Japanese television set manufacturers set 9300K as a chromaticity temperature of the reference white since the late 1950's when it began to use P22-series phosphors, and have manufactured the television sets that could achieve a color reproduction according to the chromaticity temperature of the reference white. Thereafter, in Korea or Japan where about 6000K daylight fluorescent lamps are mainly used as indoor illuminators, the television sets tend to be manufactured under conditions that the reference white is set randomly between 11000K to 13000K, which is higher than 9300K.
While a reference white, which is set to the broadcasting station and in particular to the broadcasting camera, is fixed, a reference white of the television set, particularly the display device, is not fixed but increased gradually. Therefore, the videos reproduced on the display device are distorted because of a difference between both reference whites.
Meanwhile, like aerial-wave broadcasting signals and component signals, signal sources of the television sets also have different standards from each other and various sources are actually used. Here, the aerial-wave broadcasting signals are generated from NTSC broadcasting or HDTV broadcasting, and component signals are generated from DVD or digital still camera.
Further, when transmission side of the television set performs the color reproduction without considering gamma corrected characteristic, distortions can occur in the color reproduction, and thus reproduction fidelity with respect to original colors is degraded. In addition, one important problem may be a colorimetric error, which is caused by discord between phosphor coordinates of a standard monitor of the broadcasting camera and those of the television set.
In addition to general aerial-wave broadcasting signals, the current television sets can compatibly process variously formatted signal sources (in other words, a TV signal source, a PC signal source, a component signal source, etc), such as HDTV broadcasting signals, cable broadcasting signals, PC signals, DVD signals, VCR signals, etc. Further, in addition to various conventional CRT-based display devices (Cathode Ray Tube (CRT), Cathode Display Tube (CDT), Cathode Picture Tube (CPT), etc.), flat-panel display devices (Liquid Crystal Display (LCD), Plasma Display Panel (PDP), Field Emission Display (FED), etc.) tend to be selectively applied to the display devices of the television sets. As described above, since all various signal sources and display devices are not considered, improved or optimal color reproduction cannot be achieved because of the video distortion.
Related art methods for processing video signals according to signal sources and disadvantages thereof will now be described. FIG. 1 is a schematic view of a related art video display device for processing TV signal.
Referring to FIG. 1, the related art video display device (e.g., TV set) includes a TV signal processor 10 for dividing TV signal into an audio signal and a video signal through tuning/detecting/demodulating operations of the TV signal, and an A/V switch 11 for switching the audio and video signals divided at the TV signal processor 10. A 3D comb filter 12 is for separating luminance and color signals Y/C from the video signal outputted from the A/V switch 11. A decoder 13 is for converting the luminance and color signals Y/C into a luminance and color difference signals Y, U and V, and a video/synchronization processor 14 is for performing a matrix conversion for a color space conversion with respect to the luminance and color difference signals converted at the decoder 13. An ADC 15 is for converting the luminance and color difference signals into digital video signals, a video processor 16 is for converting the digital video signals into color signals R′, G′ and B′, and a video output unit 17 is for outputting the color signals R′, G′ and B′ converted (e.g. from Y, U, V) at the video processor 16 to a display device (not shown). However, in case the luminance and color difference signals are the NTSC TV signal and A/V signals, the video/synchronization processor 14 bypasses them.
As shown in FIG. 4, when the NTSC TV signal is displayed on the display device, a color reproduction area of the signal source (i.e., the broadcasting camera) is much different from that of the display device. Thus, the original signal provided in the signal production is difficult to reproduce equally on the display device for at least reasons described below.
According to NTSC standard, an illuminant C is defined as a reference white of a camera (i.e., the signal source of TV signal). Here, the illuminant C has a color temperature of 6774K and a chromaticity coordinate given by (xws, yws, zws)=(0.3101, 0.3162, 0.337). At this time, according the definition of standard phosphor coordinates of the NTSC standard camera, standard phosphor coordinates of red, green and blue colors (R, G, B) are given by (xrs, yrs, zrs)=(0.67, 0.33, 0.00), (xgs, ygs, zgs)=(0.21, 0.71, 0.08), and (xbs, ybs, zbs)=(0.14, 0.08, 0.78), respectively.
On the contrary, the television sets have different reference white and phosphor according to the kind of display devices. For example, in case of 60″ a LCD PJT television set, its reference white has a color temperature of 9300K and a chromaticity coordinate given by (xwd, ywd)=(0.283, 0.297) and phosphor coordinates of red, green and blue colors R, G and B are given by (xrd, yrd, zrd)=(0.645, 0.35, 0.005), (xgd, ygd, ygd)=(0.279, 0.714, 0.007), and (xbd, ybd, zbd)=(0.136, 0.066, 0.798), respectively. Accordingly, the phosphor coordinates (G) of the display device are very different from the NTSC standard phosphor coordinates or digital television (TV) standard phosphor coordinates.
FIG. 4 is a diagram showing a color reproduction area and a position of the reference white according to a general signal source and a general display device. The NTSC signal source and the SMPTE signal source used as signal sources, and LCD is used as a display device.
As shown in FIG. 4, since the color reproduction area of the signal source is different from that of the display device, the original signal provided in the signal production is very difficult to reproduce equally on the display device. Additionally, since a standard gamma of the NTSC TV signal source, as shown in FIG. 14, is 2.2, the NTSC TV signal source is processed to have a characteristic of FIG. 13A and then transmitted. However, unlike a CRT, the LCD PJT television set has a S-shape gamma characteristic curve.
As described above, in case of NTSC TV signal, since reference white, phosphor coordinate and camera gamma processing of the signal sources are different from those of the display device, it is very difficult to achieve desired color reproduction. Thus, the colorimetric error occurs so that the video is displayed unnaturally in color.
FIG. 2 is a schematic view of a related art video display device for processing component signal. The component signal source can include DVD signal and DTV signal.
Referring to FIG. 2, the related art video display device includes a component signal processor 20 for processing component signals Y, PB and Pr, a video/synchronization processor 21 for performing a matrix conversion for a color space conversion with respect to the component signals Y, Pb and Pr outputted from the component signal processor 20, and an ADC 22 for converting a luminance signal Y and color signals Cb and Cr, which are outputted from the video/synchronization processor 21, into digital video signals. A video processor 23 is for processing the digital video signals into color signals R′, G′ and B′, and a video output unit 24 is for outputting the color signals R′, G′ and B′ to a display device.
According to ITU-R BT.709 standard (refer to FIG. 14), an illuminant D65 is defined as a reference white of the component signal source. The illuminant D65 has a color temperature of 6504K and a chromaticity coordinate given by (xws, yws, zws)=(0.3127, 0.3290, 0.3583). At this time, standard phosphor coordinates of red, green and blue colors R, G and B are given by (xrs, yrs, zrs)=(0.64, 0.33, 0.03), (xgs, ygs, zgs)=(0.30, 0.60, 0.10), and (xbs, ybs, zbs)=(0.15, 0.06, 0.79), respectively. Additionally, as shown in FIG. 14, DTV signal is processed with standard gamma of 2.222 and then transmitted.
At this time, the display device uses 9300K as the reference white and the phosphor coordinates are equal to the above. Accordingly, in case the component signals are processed at the related art television set and displayed thereon, the same problems can occur as described in the system of FIG. 1.
FIG. 3 is a schematic view of a related art video display device for processing PC signal. Referring to FIG. 3, the related art video display device includes a PC signal processor 30 for processing PC signals, a video/synchronization processor 31 for performing a matrix conversion for a color space conversion with respect to the PC signal outputted from the PC signal processor 30 and an ADC 32 for converting a received luminance signal Y and color signals Cb and Cr into digital video signals. The PC signals R, G and B is outputted to the video/synchronization processor 31, and the video/synchronization processor 31 performs a matrix conversion with respect to the PC signals R, G and B to output the luminance signal Y and the color signals Cb and Cr. A video processor 33 is for processing the digital video signals into color signals R′, G′ and B′, and a video output unit 34 for formatting and outputting the color signals R′, G′ and B′ to a display device.
According to sRGB standard (refer to FIG. 14), an illuminant D65 is defined as a reference white of the PC signal source. Here, the illuminant D65 has a color temperature of 6504K and a chromaticity coordinate given by (xws, yws, zws)=(0.3127, 0.3290, 0.3583). At this time, standard phosphor coordinates of red, green and blue colors R, G and B are given by (xrs, yrs, zrs)=(0.64, 0.33, 0.03), (xgs, ygs, zgs)=(0.30, 0.60, 0.10), and (xbs, ybs, zbs)=(0.15, 0.06, 0.79), respectively. As shown in FIG. 14, DTV signal is obtained through the standard gamma processing of 2.222.
Meanwhile, the display device uses 9300K as the reference white and the phosphor coordinates are equal to the above. Of course, the reference white and the phosphor coordinates of the display devices are changed according to the kind of the display devices as described above.
In case of PC signal, as described above, the colorimetric error occurs because of differences of the reference white and the phosphor coordinates between the signal source and the display device. Accordingly, the colorimetric error causes the video to be displayed incorrectly or unnaturally in color.
In the above-described signal processing methods of the related art video display devices, when signals that are generated under conditions of different reference white and phosphor coordinates at respective signal formats are displayed, the colorimetric errors occur because the reference white and phosphor coordinates of the display device were not considered. Additionally, when the gamma processed signals of the signal source are displayed without considering the gamma characteristic of the display device, the colorimetric error occurs.
In addition, the colorimetric error can occur because the standard phosphor coordinates of signal source such as TV signal, component signal and PC signals are different from those of the display devices such as CRT, CPT, LCD and PDP. In other words, the colorimetric error may be caused by discord of phosphor coordinates between the signal source and the display device. Further, the colorimetric error can occur because of a difference of gamma characteristics between the signal source and the display device.
As described above, related art video display devices have various disadvantages. Related art video display devices can receive the signal sources that have different standard phosphors and different reference white and are differently gamma-processed, and display them on the display devices that have different standard phosphors and different reference white and are differently gamma-processed. As a result, there is a long felt demand for an apparatus that can reduce the reproduction error by considering various formats of signal sources and various display devices.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.